Re: Experimental patch for inter-page delay in VACUUM

Bruce Momjian wrote:

> Jan Wieck wrote:
>> >> > If the background cleaner has to not just write() but write/fsync or
>> >> > write/O_SYNC, it isn't going to be able to clean them fast enough. It
>> >> > creates a bottleneck where we didn't have one before.
>> >> >
>> >> > We are trying to eliminate an I/O storm during checkpoint, but the
>> >> > solutions seem to be making the non-checkpoint times slower.
>> >> >
>> >>
>> >> It looks as if you're assuming that I am making the backends unable to
>> >> write on their own, so that they have to wait on the checkpointer. I
>> >> never said that.
>> >
>> > Maybe I missed it but are those backend now doing write or write/fsync?
>> > If the former, that is fine. If the later, it does seem slower than it
>> > used to be.
>>
>> In my all_performance.v4.diff they do write and the checkpointer does
>> write+sync.
>
> Again, sorry to be confusing --- I might be good to try write/fsync from
> the background writer if backends can do writes on their own too without
> fsync. The additional fsync from the background writer should reduce
> disk writing during sync(). (The fsync should happen with the buffer
> unlocked.)

No, you're not. But thank you for suggesting what I implemented.

Jan

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